GPS based devices are well known and are widely employed as in-car navigation systems. Reference may be made to the Navigator series software from the present assignee, TomTom B.V. This is software that, when running on a PDA (such as a Compaq iPaq) connected to an external GPS receiver, enables a user to input to the PDA a start and destination address. The software then calculates the best route between the two end-points and displays instructions on how to navigate that route. By using the positional information derived from the GPS receiver, the software can determine at regular intervals the position of the PDA (typically mounted on the dashboard of a vehicle) and can display the current position of the vehicle on a map and display (and speak) appropriate navigation instructions (e.g. ‘turn left in 100 m’). Graphics depicting the actions to be accomplished (e.g. a left arrow indicating a left turn ahead) can be displayed in a status bar and also be superimposed over the applicable junctions/turnings etc in the roads shown in the map itself. Reference may also be made to devices that integrate a GPS receiver into a computing device programmed with a map database and that can generate navigation instructions on a display. The term ‘navigation device’ refers to a device that enables a user to navigate to a pre-defined destination. The device may have an internal system for receiving location data, such as a GPS receiver, or may merely be connectable to a receiver that can receive location data.
PDAs often employ touch screens to enable a user to select menu options or enter text/numbers using a virtual keyboard. Generally, touch input is meant to occur using a thin stylus since the size of individual virtual keys or other selectable items is relatively small. When navigating from a screen relating to one function or type of functions in an application to a different function or type of functions, then the presumption is that stylus selection of virtual keys, control panels, check boxes etc. will be undertaken since the related touch control zones are relatively small.
However, with some individual applications, such as a calculator application, each numeric may key be large enough to be selectable using a finger, as opposed to the stylus. However, where a large number of keys needs to be displayed at the same time (e.g. for a QWERTY or other format virtual keyboard with all alphabet letters), then a far smaller virtual keyboard has to be used; individual keys have then to be selected with the stylus. Hence, prior art devices may mix large, numeric keys available on one screen with much smaller keys on a different screen, even though the keys are of equal importance. Core functions cannot be said to be uniformly and consistently designed for effective and reliable finger operation, because the assumption is that users will operate a stylus on most occasions.